A bug in Apple's HealthKit -- a back-end feature in iOS 8 -- is delaying the launch of outside developers' fitness and health apps, the company said Wednesday.

HealthKit is a new tool for developers in iOS 8 designed to let their apps talk to Apple's native health apps. HealthKit is meant to pull in information from other apps and devices, like calories burned or heart rate, and make it more useful. For instance, it could allow a nutrition app, with the user's permission, to tell other fitness apps how many calories the person consumes in a day, Apple says.

It can also let data like blood pressure be shared automatically with a doctor.

"It just might be the beginning of a health revolution," as Apple calls it.

The revolution, apparently, can wait. In a statement, Apple said it had discovered a bug in the system, preventing the release of compatible apps as scheduled for Wednesday alongside the launch of iOS 8.

"We're working quickly to have the bug fixed in a software update and have HealthKit apps available by the end of the month," a spokeswoman said via email.

Developers had planned to release new versions of their apps for HealthKit on Wednesday. The launch of at least one fitness app, Carrot Fit, apparently did not go as planned. "Just want today to be over with," said developer Brian Mueller in a tweet later on Wednesday, after re-submitting the app to Apple.

HealthKit is separate from Apple's new Health app in iOS 8, which gives users a viewable dashboard of their health and fitness data. That app appeared to be functioning fine on Wednesday.

The HealthKit bug and app delay is an unfortunate development for Apple as the company tries to make a new push into health and fitness. The company's new Apple Watch also includes sensors and apps for health tracking, generating data that can be synced to people's iPhones.